Subject: Re: [mobile-ip] issues 92, 94, 95 and text for sending BAs with R H

From: Erik Nordmark <[email-masked]>
Date: Mon, 9 Sep 2002 23:40:48 +0200 (CEST)

> FWIW, I agree with Hesham.  Site-Locals are not trivially handled
> if the HA is multi-sited (it's a little easier on MN).  So, for the
> sake of simplicity of the protocol (which is already rather
> complex), let's remove the site-local use.

What does "remove site-local use" mean? Require that site-local
addresses must not be used for HoA and/or CoA?

IMHO that would be throwing the baby out with the bathwater.

Supporting site-local addresses on multi-sited nodes (whether HAs, routers,
or just hosts) is a fair amount of complexity.
But one of the uses of site-local addresses (perhaps the only reasonable use?)
is for sites that are not connected to the Internet hence does not have
any global addresses. Preventing such a site from using Mobile-IPv6 internally
seems to be broken.

If we want to limit the complexity of site-locals it would be better to argue 
that HAs should never be multi-sited.

  Erik

---

From: Jari Arkko <[email-masked]>
Date: Tue, 10 Sep 2002 10:58:19 +0300

> that HAs should never be multi-sited.

This would be a reasonable limitation. However, is it enough? Let's talk about
site-local home addresses. Assume an MN has one. Everything is OK as long as
the MN stays within the site as you propose above. But what if the MN happens
to go outside the site? Say, it accidentally connects to someone else's WLAN.
How should it behave with its site-local home address? Perhaps it could still
connect to its HA with the bidirectional tunnels. It can't talk to CNs in the
visited site, because (a) it can't get to them via the bidirectional tunnel
and (b) if it tries to establish RO it will fail due to HOTI/HOT never reaching
the right CN. Hmm... perhaps everything is safe from the point of view CNs
then. The only strange thing is that the BUs going between the MN and the HA
will have a site-local HAO, and it is not clear how they might be treated
by firewalls and filters.

And then to site-local care-of addressses. Currently, these are not forbidden
in the specification. If the local router advertises a site-local prefix, the
MN could get a site-local care-of address. Under which conditions can we use
this address? Only if the HA is within the same site. But it isn't clear to
me how the MN would know if it is in the same or different site. So it might
be safer to assume that at the very least the MN should try to use a global
address as a care-of address, if it has a choice. If it does not have a choice,
it could also use the site-local address.

Jari

---

From: Erik Nordmark <[email-masked]>
Date: Tue, 10 Sep 2002 10:41:26 +0200 (CEST)

> This would be a reasonable limitation. However, is it enough? Let's talk
> about site-local home addresses. Assume an MN has one. Everything is OK as
> long as the MN stays within the site as you propose above. But what if the MN happens
> connect to its HA with the bidirectional tunnels

Given that my example was an isolated site (not connected
to the Internet), the MN can't move outside the
site and expect anything.

Forbidding site-local HoAs means that MIPv6 can't be used in an isolated site.
Do we really want to forbid that?

  Erik

---

From: Jari Arkko <[email-masked]>
Date: Tue, 10 Sep 2002 12:49:40 +0300

> site and expect anything.

Yes. But since the our specifications can't really prevent
from this happening in the real world some day, what I was
trying to do was to figure out if it would lead to a catastrophy
or not. It seems that going outside the original site would
not cause any major problems. But it also seems that we may
have to be a bit careful with the care-of address selection
if multiple kinds of addresses are available. Perhaps it is
sufficient to add the following things to the specification:

- Require that home agents and mobile nodes that use site-local
   addresses always stay completely within that site.
- Pick a global care-of address if available.

Jari

---

From: Erik Nordmark <[email-masked]>
Date: Tue, 10 Sep 2002 13:55:08 +0200 (CEST)

> - Pick a global care-of address if available.

Yes, that should be sufficient. 
(I would phrase the first bullet differently
since you can't actually require that the nodes not move. Pointing out
that MIPv6 can not and does not provide transparent communication
when site-local addresses are used and the MN move outside the site
would be my way of phrasing it).

Then, independently, the complexity of the IPv6 site-local addresses
for multi-sited nodes can be discussed independently of MIPv6
in the ipng (or v6ops?) WG.

  Erik

---

From: Francis Dupont <[email-masked]>
Date: Tue, 10 Sep 2002 14:25:36 +0200

=> proposal: forbid use of addresses with a limited scope when
addresses with a larger scope are available (i.e., use
the maximal possible scope)?

[email-masked]

---

From: "James Kempf" <[email-masked]>
Date: Tue, 10 Sep 2002 08:21:56 -0700

> it could also use the site-local address.

Site local CoAs could also be used with LMM, as long as the LMM agent/MAP is
within the site.

            jak

---

From: "James Kempf" <[email-masked]>
Date: Tue, 10 Sep 2002 08:29:12 -0700

> - Pick a global care-of address if available.

I'd like to see these critera reflect the possibility of using a site local for
a LCoA with an LMM agent.

            jak